Source:
J.edlow, E-medicine, and
www.adam.com

Background: Tularemia is an infectious disease caused by the gram-negative pleomorphic bacterium, Francisella tularensis. The disease was first described in Japan in 1837. Its name relates to the description in 1911 of a plague-like illness in ground squirrels in Tulare county, California and the subsequent work done by Dr. Edward Francis. In 1928, he described his personal experience with over 800 cases.

Francisella tularensis is found worldwide in over a hundred species of wild animals, birds and insects. It produces an acute febrile illness in humans. The route of transmission and factors relating to the host and the organism influences the presentation.


Pathophysiology:
Tularemia is classically divided into several forms (ulceroglandular, glandular, oculoglandular, oro-pharyngeal, pneumonic and typhoidal), each form reflecting the mode of transmission. The organism gains access to the host by inoculation into skin or mucous membrane, by inhalation or by oral ingestion.

Some authorities simplify this classification into just two groups, the far more common ulceroglandular form (in which local or regional symptoms and signs predominate) and the more lethal typhoidal form (in which systemic symptoms dominate the clinical picture).

The skin is the portal of entry in ulceroglandular tularemia. The organism passes through cut or abraded skin (sometimes clinically inapparent) or enters via tick or insect bite. An inoculun of as few as 10 organisms subcutaneously can cause disease. The conjunctiva can be the portal of entry from a splash with infectious material (for example blood from a rabbit carcass) or from rubbing the eyes with contaminated hands.

After an incubation period of 3-4 days (range 1-14), a papule develops and the patient develops a high fever. The papule evolves into an ulcer associated with regional lymphadenopathy. Some patients infected by a second, less virulent strain (Type B), present less dramatically.

While numerous animals and insects can carry F. tularensis, rabbits and ticks (especially Dermacentor and Amblyomma species) are most commonly implicated in human cases. The deer fly is another classic, although a less common, vector.

The organism can be inhaled, which may lead to pneumonic tularemia. Alternatively, organisms can be ingested which may cause oro-pharyngeal tularemia and, possibly, some cases of the typhoidal form. In most typhoidal tularemia, the portal of entry remains unknown.

Frequency:

  • In the US: A few hundred cases of tularemia are reported annually in the U.S. As with most such diseases, the majority of cases are likely unreported or misdiagnosed. While sporadic cases occur in all states, those with the highest prevalence are Arkansas, Illinois, Missouri, Texas, Oklahoma, Utah, Virginia and Tennessee.

    The frequency of tularemia has dropped markedly over the last 50 years and there has been a shift from winter disease (usually from rabbits) to summer disease (more likely from ticks).

  • Internationally: Tularemia is found worldwide, but its incidence is unknown.

Mortality/Morbidity: Untreated, tularemia carries a mortality rate of 5-15%; even higher with the typhoidal form. Appropriate antibiotics lower this rate to about 1%.


Sex: Biologically there is no sex bias; however, the types of activities that predispose to tularemia (e.g., tick bites, rabbit and wild game exposure), generally occur in young to middle-aged men.

History: Tularemia is classically divided into 6 categories. The first is the ulceroglandular form (70-80% of cases) in which the organism enters via a scratch or abrasion and spreads via the proximal lymphatics. Within the ulceroglandular form there is even more differentiation. In the glandular form, there is no ulcer and the organism is presumed to have gained access to the lymphatics and/or bloodstream via clinically inapparent abrasions.

The second form is the oculoglandular form (1% of cases), in which the organism enters via the conjunctiva from either splashing of infected blood or rubbing the eyes after contact with infectious materials.

The third form is the oropharyngeal form (rare) that occurs after ingestion of the organism from eating undercooked rabbit meat.

The fourth form is the pneumonic form (uncommon), which occurs when the organism is inhaled. This is seen in laboratory workers and, occasionally, occurs naturally. Pneumonia also occurs in 10-15% of patients with ulceroglandular tularemiaand in one-half of those patients with typhoidal tularemia.

The final form is the typhoidal (or septicemic) form (10-15% of cases). This is a more severe form, which often includes pneumonia.

  • Ulceroglandular and Glandular Forms:
    • In this form, the patient complains of an ulcer at the site of inoculation.
    • In rabbit-associated cases, the ulcer is usually on the fingers or hand.
    • In tick-associated cases, common sites include the groin, axillae and trunk. Regional swollen glands will reflect this same geographical pattern. The infected nodes are painful.
    • The glandular form is distinguished from the ulceroglandular form by the absence of an ulcer. This presumably occurs when the bacterium gains entry via microscopic abrasions.
  • Oculoglandular Form:
    • The patient complains of a painful, red eye, often with purulent exudate.
    • They may note swollen glands in the submandibular, preauricular or cervical areas.
  • Oropharyngeal Form:
    • The abdominal pain is caused by mesenteric adenopathy and the bleeding results from intestinal ulcerations.
  • Pneumonic Form:
    • In this form, produced by inhalation of organisms or by hematogenous spread from ulceroglandular or typhoidal disease, patients complain of dry cough, dyspnea and pleuritic chest pain.
    • Some patients with tularemic pneumonia develop systemic symptoms without the above respiratory complaints.
  • Typhoidal (Septicemic) Form:
    • This is essentially a F. tularensis bacteremia and presents with fevers, chills, myalgias, malaise and weight loss.
    • The absence of ulcer or lymphadenopathy makes diagnosis difficult.

Physical: The physical findings in tularemia also vary with the mode of presentation.

  • Findings common to most cases are fever, tender hepatosplenomegaly and, in about 20% of patients, a generalized maculopapular rash that occasionally becomes pustular.
  • Erythema nodosum occurred in 4 out of 88 cases in one series.
  • The ulcer forms at the site of the skin entry of the organism. The location (see above) varies with the vector.
    • The lesion starts as a tender papule that evolves into an ulcer with sharply demarcated borders and exudate.
    • Regional nodes are edematous, tender, can become fluctuant and may drain spontaneously.
  • Ocular Findings:
    • Unilateral intensely injected conjunctiva with purulent exudate
    • Ulcerations and nodules on the palpebral conjunctiva
    • Preauricular and cervical adenopathy are seen and corneal ulceration is reported.
  • Exudative and membranous pharyngitis with regional adenopathy may be seen with the oropharyngeal form.
  • In the pneumonia form, rales are sometimes heard, but a normal lung examination is not uncommon.
  • The physical findings associated with pericarditis, peritonitis, meningitis and osteomyelitis can be seen when these rare manifestations exist.


Causes:
Tularemia is caused by infection with the bacteria, Francisella tularensis.



Treatment: 


Emergency Department Care:

  • Tularemia must be considered in patients with fever and regional lymphadenopathy, particularly when an ulcer or conjunctivitis is present.
  • The typhoidal form presents as a non-specific febrile illness with little to suggest tularemia in the absence of a careful epidemiologic history.
  • In these latter patients, other potentially life-threatening infections should be considered and excluded or treated as appropriate.

Consultations: Consultation with an infectious disease specialist is often indicated.


Further Outpatient Care:

  • Any patient being treated as an outpatient for tularemia should have close follow up, preferably with a primary care physician.

Deterrence/Prevention:

  • When hunting rabbits, skinning or preparing rabbit carcasses, great care must be taken to avoid touching the rabbit blood and flesh. Avoid touching the eyes while performing the above activities. Wash hands thoroughly after finishing.


Complications:

Prognosis:

  • Roughly 5-15% of untreated patients succumb to the disease.
  • Factors associated with increased mortality include typhoidal presentation, elevated CPK levels, renal failure, late diagnosis or other serious co-morbidities.

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